Optical absolute encoder
Hengstler ACURO AX73 optical absolute encoder
Explosion-proof absolute encoder with a 22-bit optical sensor in a 76 mm stainless steel housing, certified for gas and dust atmospheres, IP67 and rated -40 to +70 °C, with SSI, BiSS-B, BiSS-C or PROFIBUS.
Key specifications
| Ingress protection | IP67 |
|---|---|
| Temperature | -40–70 °C |
| Data / bus | SSI, BiSS-B, BiSS-C, PROFIBUS |
| Resolution (max) | 22 bit |
| Housing | 76 |
| Approvals | ATEX / IECEx gas and dust explosion protection (zones not stated on the page read) |
| Housing | stainless steel |
Summarised in our own words from Ralliant Corporation (Hengstler GmbH, part of Hengstler-Dynapar)'s published data; series maxima, individual models vary. Last checked 2026-10-30. Source 1
Specify Motion is not affiliated with Ralliant Corporation (Hengstler GmbH, part of Hengstler-Dynapar). Hengstler and ACURO AX73 are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a Hengstler part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 3 series from our supply network are the closest match on published figures.
Harsh-environment hollow-shaft Electric Encoder with higher shock/vibration tolerance; tested to MIL-STD-810.
| Published maximum | ACURO AX73 | VLP |
|---|---|---|
| Resolution | 22 bit | 23 bit meets or exceeds |
Ultra-thin single-turn hollow-shaft capacitive encoder for general robotics and automation, with push-button calibration.
| Published maximum | ACURO AX73 | VLX |
|---|---|---|
| Resolution | 22 bit | 23 bit meets or exceeds |
Extreme-temperature hollow-shaft encoder rated from -55 C to +125 C for aerospace.
| Published maximum | ACURO AX73 | VLT |
|---|---|---|
| Resolution | 22 bit | 23 bit meets or exceeds |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
What an optical absolute encoder is
An optical absolute encoder reads a unique code pattern on a disc or scale, so every position has its own digital value and position is known immediately at power-up. Single-turn encoders give position within one revolution; multi-turn encoders also count revolutions using gears or electronic counters. Position is sent over a serial interface such as SSI or BiSS, a manufacturer-specific protocol, or a fieldbus. Optical scanning gives high resolution, typically 17 bits per revolution or more in servo encoders, and good accuracy.
When engineers choose an optical absolute encoder
Choose an optical absolute encoder where knowing position at power-up matters, such as robots, machine tools, multi-axis machines and axes that cannot be homed safely. It removes homing routines and supports safety functions. The trade-offs are cost, interface compatibility and contamination sensitivity. Battery-backed multi-turn types need battery maintenance; gear or energy-harvesting types avoid that. In very dirty environments, magnetic or inductive absolute encoders may suit better.
How to specify the Hengstler ACURO AX73
Send these with your enquiry and an engineer can confirm the right ACURO AX73 variant or an equivalent:
- Single-turn resolution (bits)
- Multi-turn range (revolutions)
- Interface: SSI, BiSS, proprietary serial or fieldbus
- Accuracy (arcsec)
- Shaft or hollow shaft size (mm)
- Speed (rpm)
- Environment and safety rating
Common mistakes to avoid
- Choosing an interface the drive does not support
- Forgetting battery maintenance on battery-backed multi-turn types
- Confusing resolution with accuracy
- Ignoring cable length limits for serial interfaces
Hengstler ACURO AX73: frequently asked questions
What is the Hengstler ACURO AX73?
Explosion-proof absolute encoder with a 22-bit optical sensor in a 76 mm stainless steel housing, certified for gas and dust atmospheres, IP67 and rated -40 to +70 °C, with SSI, BiSS-B, BiSS-C or PROFIBUS. Published series figures include temperature -40 °C, temperature 70 °C, resolution 22 bit. It is made by Ralliant Corporation (Hengstler GmbH, part of Hengstler-Dynapar); Specify Motion can help source it or propose an equivalent.
Who makes the Hengstler ACURO AX73?
The Hengstler ACURO AX73 is made by Hengstler (Ralliant Corporation (Hengstler GmbH, part of Hengstler-Dynapar)) and is listed here for engineers comparing options. Specify Motion is not affiliated with Ralliant Corporation (Hengstler GmbH, part of Hengstler-Dynapar); brand names are used only to identify the product.
What is the temperature of the Hengstler ACURO AX73?
The published series minimum temperature is -40 °C. Individual models and sizes in the ACURO AX73 range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the Hengstler ACURO AX73?
Yes. On published figures, Netzer Precision VLP and Netzer Precision VLX are the closest match from our supply network. An engineer confirms the fit against your application before recommending anything.
What is the difference between single-turn and multi-turn absolute encoders?
A single-turn absolute encoder knows its angle within one revolution. A multi-turn absolute encoder also counts complete revolutions, so it knows total position over many turns even after power loss. Multi-turn encoders avoid homing on axes driven through screws or gears.
Which interface should an absolute encoder use?
Use the interface supported by the drive or controller. SSI is simple and widely supported, BiSS-C is an open bidirectional protocol, and several manufacturer-specific protocols are common on machine tools and servo drives. Fieldbus encoders suit PLC networks. Check cable lengths and update rates for the control loop.
Further reading: Absolute vs incremental encoders · How to select an encoder · Encoders and feedback
Other optical absolute encoder series
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